Reducing power consumption of circuits to increase battery life is one of the main design concerns especially in portable applications. In many serializer/deserializer (SerDes) designs like those complying with backplane standards, such as M-PHY, a low-swing differential output driver scheme can achieve low power consumption and good signal integrity. In this scheme, there are two types of output drivers, a current-mode driver and a voltage-mode driver. Compared with current-mode drivers, voltage-mode drivers are more power efficient by using less current to get the same output voltage swing. Voltage-mode drivers may have differential outputs and/or single ended outputs.
In voltage-mode driver design, one of the design challenges is how to set the active output resistance or impedance to match with the proper termination impedance in both differential and single-ended output to meet design specifications. For example, proper termination impedance can enable the voltage-mode driver to meet the specifications on return loss, output common mode voltage, and single-ended/differential output resistance. Previous solutions set differential output resistance to proper termination impedance. However, previous solutions fail to balance the single-ended output resistance and cannot be set to achieve proper termination impedance. This failure can cause common-mode voltage shift, different reflection on different output lines and even cause the single-ended output resistance to drift outside the specification. Accordingly, a need exists for an improved integrated circuit and an improved method of controlling output impedance.